Ap2337, 0a single channel current-limited load switch, New prod uc t – Diodes AP2337 User Manual
Page 8
AP2337
1.0A SINGLE CHANNEL CURRENT-LIMITED LOAD SWITCH
AP2337
Document number: DS35060 Rev. 2 - 2
8 of 10
October 2011
© Diodes Incorporated
NEW PROD
UC
T
Application Note (cont.)
Thermal Protection
Thermal protection prevents the IC from damage when the die temperature exceeds safe margins. This mainly occurs when
heavy-overload or short-circuit faults are present for extended periods of time. The AP2337 implements a thermal sensing to
monitor the operating junction temperature of the power distribution switch. Once the die temperature rises to approximately
150°C, the Thermal protection feature gets activated as follows: The internal thermal sense circuitry turns the power switch
off thus preventing the power switch from damage. Hysteresis in the thermal sense circuit allows the device to cool down to
approximately 20°C before the output is turned back on. This built-in thermal hysteresis feature is an excellent feature, as it
avoids undesirable oscillations of the thermal protection circuit. The switch continues to cycle in this manner until the load
fault is removed, resulting in a pulsed output.
Discharge Function
When input voltage is pulled, the discharge function is active. The output capacitor is discharged through an internal NMOS
that has a discharge resistance of 100
Ω. Hence, the output voltage drops down to zero. The time taken for discharge is
dependent on the RC time constant of the resistance and the output capacitor. Discharge time is calculated when UVLO
falling threshold is reached to output voltage reaching 300mV.
Power Dissipation and Junction Temperature
The low on-resistance of the internal MOSFET allows the small surface-mount packages to pass large current. Using the
maximum operating ambient temperature (T
A
) and R
DS(ON)
, the power dissipation can be calculated by:
P
D
= R
DS(ON)
× I
2
Finally, calculate the junction temperature:
T
J
= P
D
x R
θJA
+ T
A
Where:
T
A
= Ambient temperature °C
R
θJA
= Thermal resistance
P
D
= Total power dissipation
Ordering Information
AP 2337 SA - 7
7 : Tape & Reel
Package
Packing
SA : SOT23
Device
Package Code
Packaging
(Note 7)
7” Tape and Reel
Quantity
Part Number Suffix
AP2337SA-7
SA
SOT23
3000/Tape & Reel
-7
Notes:
7. Pad layout as shown on Diodes Inc. suggested pad layout document AP02001, which can be found on our website at